Temperature regulated tuning fork



Patented Sept. 26, 1939 UNITED STATES PATENT OFFICE TEMPERATURE REGULATED TUNING FORK Application April 25, 19739, Serial N0. 269,914

9 Claims.

This invention relates `to tuning forks and more especially to forks whose vibrational frequency is substantially independent of ambient temperatures.

A principal object is to provide a temperatureregulated tuning fork which is of compact design rendering it particularly suitable for use in portable equipment.

Another object is to provide a temperatureregulated tuning fork which has a high degree of frequency stability rendering it suitable for use in remote synchronizing apparatus, for example facsimile machines and the like.

A feature of the invention relates to an electromagnetically driven tuning fork which is provided With a novel arrangement of the magnet cores whereby the volumetric space occupied by the complete unit is materially reduced without sacrificing precision of frequency control.

Another feature relates to an electromagnetically driven tuning fork having a special arrangement of the magnetic core whereby the greater efficiency in the frequency control is obtained. In accordance with this feature, the core is formed in part of a U-shaped permanent magnet and in part of one or more bridging laminations.

Another feature relates to an electromagnetically driven tuning fork having U-shaped driving and pick-up magnets with the` legs of the U provided with portions bent back upon themselves so that substantially only the pole piece portions are located in the plane of vibration of the fork tines.

Another feature relates to a novel form of magnet arrangement for electromagnetically driven tuning forks wherein the driving and pickup coils are provided each with a permanent magnet having a return path for the magnetic lines of force independent of the fork tines, this path being proportioned so as to provide relatively high reluctance for the polarizing flux but offering very little reluctance to the alternating signal between the fork tines and the coils.

A further feature relates to the novel organization, arrangement and relative location of parts which constitute a compact, efficient and highly accurate temperature controlled tuning fork.

Other features and advantages not specifically enumerated will be apparent after a` consideration of the following detailed descriptions and the appen-ded claims.

While the invention will be described in one preferred embodiment, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention. Accordingly in the draw- Fig. 1 is a vertical elevational View of the temperature controlled tuning fork assembly according to the invention with part of the heat insulating wrapper broken away.

Fig. 2 is a central vertical sectional View of Fig. l.

Fig. 3 is a right-hand side View of Fig. 2 with the housing removed and with certain parts broken away.

Fig. 4 is a sectional view of Fig. 2 taken along the line 4-4.

Fig. 5 is a vertical bottom View of Fig. 3.

The fork comprises the usual yoke portion I, and the tines 2, 3, which may be made of any suitable magnetic material such for example aS an alloy sold under the trade-name Invar and having nickel and iron as its principal components and having an extremely low expansion coefficient. The yoke is preferably formed with a flat face 5 which is slightly spaced from the corresponding flat face 6 of a U-shaped supporting frame having the parallel vertical Standards l, 8 and yoke 9. This frame is preferably formed of a non-magnetic material of good heat conductivity for example aluminum or the like. The fork is rigidly fastened against the flat face of standard 8 by a bolt I0 and nut Il. If desired, one or more spacing members or shims i2 may be provided to space the fork properly with relation to the frame. Each of the standards "I, 8, has a window I3, I4, located approximately in alignment with the face I5 of yoke I, so that by inserting a suitable tool such as a file, the effective length of the fork tines can be adjusted, for example by filing away the face I5.

Fastened to standard 8 by a screw I6 and cooperating threaded washer Il, is a small U-shaped permanent magnet I8 located with its legs extending parallel to the plane of vibration of the fork tines 2 and 3. Preferably screw I6 and washer Il are of brass or other non-magnetic material. Fastened to the ends of the permanent magnet legs are extensions I9, 20, of iron, steel or other magnetic material. Extensions I9, 2i), may be fastened to the legs of the permanent magnet by a clamping arrangement comprising the parallel brass bars 2l, 22, and the three screws 23, the said members I9 and 20 being fastened between the bar 22 and the faces of the permanent magnet. Extensions I9 and 20 are bent back on themselves as shown in Fig. 4 into close proximity to the tine 3.

In order to increase the solenoid core cross section, a, pile-up of short laminations 24 is assembled on the reversely extending ends of each of the members I9 and 20. Preferably one or more of these additional laminations is in the form of a U as indicated by numeral 25 so as to provide a partial return path for the polarizing flux from the permanent magnet. However, the reluctance of this bridge path 25 is suiciently low for the alternating controlling currents so as not to reduce materially the alternating excitation of the pole pieces which face the fork tine 3. Each pole piece is therefore constituted of the solid extensions I9, 2U, the laminated pile-ups 24 and one or more of the U- shaped laminations 25. Mounted on each pole piece is a winding or solenoid 26, 21, and these windings may be connected in series or in parallel. rIhe ends of the windings are connected by wires 28, 29, to connector tabs 30, 3|, carried by an insulating bridge 32, fastened to standards l and 8. Preferably the yoke or bridge of the U-shaped lamination 25 is bent back at right angles and a layer of insulation 33 is inserted to prevent short-circuiting of the windings 26, 2'1.

The other tine 2 is provided with a similar electromagnetic arrangement including a permanent magnet having reversely bent pole pieces with corresponding windings and the parts of this other electromagnetic arrangement corresponding to those associated with tine 3 as above described, bear the same numerals which are primed. The lower ends of the standards 'l and 8 are rigidly bridged by a non-magnetic metal cross-piece 34 fastened in place by screws 35. Member 34 is provided with a window 3B in approximate alignment with the tine ends so that by inserting a suitable tool such as a file through the window 36, the mass of the tine ends may be reduced by ling in order to adjust the characteristics of the fork.

In accordance withwell-known procedure, one set of windings 25, 21, may be used as the exciting windings for maintaining the fork in continued vibration at its natural period, and the other set of windings 26', 2l', may be used as pick-up windings for leading off a current controlled by the frequency of vibration of the fork tines.

Preferably the vertical side faces of standards and 8, are curved as shown in Fig. 4, and fastened by bolt 3l to the upper end is a circular closure member 38 having a shouldered rim which rests on the edge of the closely tting cylindrical housing 39, which is completely closed at its lower end. The fork assembly may then be fastened in place within the housing by screws 40.

Preferably the cover member 38 carries four binding posts 4l insulated therefrom, these binding posts being connected to the respective lugs 3U, 3i, whereby the exciting magnets for the fork are connected in a suitable circuit and the pick-up magnets for the fork are connected in a suitable circuit.

In order to maintain the fork at a uniform temperature, there is attached to the housing S9, for example by soldering or welding a tubular metal member 42 to receive any well-known form of thermostat circuit controlling device 43. 'Ihe entire assembly is then enclosed in an electric heating element 44 which is insulated from the housing 39 and member 42 by a layer 45 of mica or the like. The heating element may be wrapped around with a layer of asbestos 46 and held in place by suitable clamping bands 47, 48, the terminals for the heating element being indicated at 49, 50. If desired, a strip 5I of insulation may be fastened to the housing 39 and provided with a series of contact lugs 52 whereby the connections to the thermostat and the heater element may be completed. In accordance with well-known practice, the thermostat may be set for a given temperature so that it operates to close the circuit of the heating element 44 only when the temperature of the fork starts to drop below a certain predetermined temperature. When the temperature of the fork has been raised to its predetermined temperature, the thermostat automatically breaks the circuit of the heating element.

The above described arrangement provides a very compact fork assembly and an eiicient magnectic drive and magnetic pick-up arrangement for association with the fork tines. By reason of the compactness of the assembly, it is capable of -being incorporated in portable equipment without sacrificing the desired degree of frequency stability of the fork. It will be obvious that various changes and modifications may be made in the materials and parts without departing from the spirit and scope of the invention.

What I claim is:

l. An electromagnetic tuning fork device comprising a tuning fork, a U-shaped magnet mounted in laterally spaced relation to the fork tines, a pair of reversely bent pole pieces having their pole faces closely adjacent the fork tines, and a magnetic bridging member located across the pole pieces.

2. An electromagnetic tuning fork device comprising a tuning fork, a U-shaped magnet mounted laterally adjacent the fork tines and having pole pieces each comprising a reversely bent member with the reversely bent ends facing the fork tines, a pile-up of laminations carried by each reversely bent end to increase the solenoid core cross section, and a magnetic bridge across said reversely bent ends.

3. An electromagnetic tuning fork device according to claim 2` in which said bridge is in the form of a U-shaped lamination.

4. An electromagnetic tuning fork device comprising a rigid supporting frame including a base and a pair of parallel uprights, a tuning fork fastened within and to said frame so that the plane of vibration of the fork tines is substantially perpendicular to the plane of said uprights, a

pair of magnets are fastened to the said uprights and located between said uprights and the fork tines, each of said magnets having a reversely bent pole piece the ends of which face the associated fork tines.

5. A tuning fork device according to claim 4 in which a removable bridge rigidly unites the ends of said uprights.

6. A tuning fork device according to claim 4 in which the frame and fork assembly are enclosed in a closely fitted metal housing carrying a thermostat, and an electric heating unit is wrapped around the exterior of said housing.

7. A tuning fork device according to claim 4 in which each of said uprights is provided with a Window adjacent the fork yoke to enable the effective length of the fork tines to be adjusted Without removing the fork from the frame.

8. A tuning fork device according to claim 4 ,75

in which a bridge member rigidly connects the ends of said uprights and is provided with a window to enable the fork tines to be adjusted Without removing the fork from the frame.

9. An electromagnetic tuning fork device comprising a tuning fork, a pair of magnets disposed on opposite sides of the fork laterally adjacent to the fork tines, each of said magnets having a reversely bent pole piece having its pole face closely adjacent one of the fork tines, and a solenoid winding on said pole piece, each magnet being of the permanent magnet type and being provided with pole pieces having laminated end sections on which said solenods are supported.

AUSTIN G. COOLEY. 

